This non-provisional application claims priority under 35 U.S.C. §119(a) on Korean Patent Application No. 2004-46177 filed on Jun. 21, 2004, which is herein expressly incorporated by reference, and on Korean Patent Application No. 2005-47107 filed on Jun. 2, 2005, which is herein expressly incorporated by reference.
1. Field of the Invention
The embodiments of the present invention relate to a composition for forming an organic insulating film and a method for forming a pattern of an organic insulating film using the composition. More particularly, the embodiments of the present invention relate to a photo-patternable composition for forming an organic insulating film which comprises: (i) a functional group-containing monomer; (ii) an initiator generating an acid or a radical upon light irradiation; and (iii) an organic or inorganic polymer, and a method for forming a pattern of an organic insulating film using the composition.
2. Description of the Related Art
Since polyacetylenes as conjugated organic polymers exhibiting semiconductor characteristics were developed, organic semiconductors have been actively investigated as novel electrical and electronic materials in a wide variety of applications, e.g., functional electronic and optical devices and various synthetic processes, because of easy molding into fibers and films, superior flexibility, high conductivity and low manufacturing costs.
Among devices fabricated using these electrically conductive polymers, research on organic thin film transistors fabricated using organic materials as semiconductor active layers has been conducted since the 1980's. In this connection, a number of studies are now being actively undertaken around the world. Organic thin film transistors are substantially identical to silicon (Si) thin film transistors in terms of their structure, but have a great difference in that organic materials are used as semiconductor materials instead of silicon. In addition, such organic thin film transistors have advantages in that they can be fabricated by printing processes at ambient pressure, and further by roll-to-roll processes using plastic substrates, instead of conventional silicon processes, such as plasma-enhanced chemical vapor deposition (CVD), making organic thin film transistors economically advantageous over silicon thin film transistors.
Organic thin film transistors are expected to be useful for driving devices of active displays and plastic chips for use in smart cards and inventory tags, and are comparable to α-Si thin film transistors in terms of their performance. The performance of organic thin film transistors is dependent on the degree of crystallization of organic active layers, charge characteristics at the interfaces between substrates and organic active layers, carrier injection ability into the interfaces between source/drain electrodes and organic active layers.
There have been a number of trials to improve the performance of organic thin film transistors. Particularly, in an attempt to decrease a threshold voltage, insulators having a high dielectric constant, for example, ferroelectric insulators, such as BaxSr1-xTiO3 (barium strontium titanate (BST)), Ta2O5, Y2O3, TiO2, etc., and inorganic insulators, such as PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNBx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3, Bi4Ti3O12, etc., have been used as materials for inorganic insulating films (U.S. Pat. No. 5,946,551). However, these inorganic oxide materials do not have a significant advantage over conventional silicon materials in terms of processing.
As materials for organic insulating films, polyimide, benzocyclobutene (BCB), photoacryl, and the like have been used (U.S. Pat. No. 6,232,157). However, since these organic insulating films exhibit unsatisfactory device characteristics over inorganic insulating films, they are unsuitable to replace inorganic insulating films.
In addition, Infineon Technology attempted to improve the chemical resistance of an organic insulating film in a subsequent process by mixing polyvinylphenol (PVP) with polymelamine-co-formaldehyde. However, this attempt is limited in its application to plastic substrates since a temperature as high as 200° C. is required to crosslink the PVP (Journal of Applied Physics 2003, 93, 2977 & Journal of Applied Physics 2002, 81, 289).
On the other hand, in order to apply organic thin film transistors to the display devices, it is necessary to form patterns of organic insulating films for the interconnection of electrodes. Photolithography has typically been employed to form patterns of organic insulating films. For photolithography, organic insulating films must satisfy the following additional requirements. That is, the organic insulating films must be compatible with photoresists. In addition, the organic insulating films must have superior thermal resistance and etch resistance to the photoresists so as not to be influenced by heating and etching during photolithography. Furthermore, the organic insulating films must have sufficient chemical resistance against a photoresist stripper to avoid the influence of the stripper when being exposed.
In the choice of suitable compositions for forming organic insulating films, the above-mentioned requirements should be taken into consideration. Accordingly, the compositions are very limited in their use. The choice of unsuitable compositions inevitably causes poor electrical properties and makes the fabrication of organic thin film transistors by all wet processes difficult. Thus, there exists a need in the art for a method for forming a pattern of an organic insulating film in a simple manner without the use of a photoresist.
In this connection, J. Vac. Sci. Technol. B, Vol. 14, No. 6, November/December 1996 describes a method for transferring a pattern by coating a resist on a substrate, imprinting the resist by molding, demolding, and removing the remaining resist by etching. However, this method has the limitation that it is not applicable to organic thin film transistors.
Microelectronic Engineering, 67-68 (2003), 845-852 discloses a method for forming a pattern of source/drain electrodes by forming a SiO2 insulating film on a Si substrate, forming metal electrodes on the insulating film by deposition, coating a polymethylmethacrylate (PMMA) resist on the electrodes, followed by molding and etching. However, the application of this method is limited to patterns of source/drain electrodes.